1. Field of the Invention
The present invention relates generally to the electronic storage, retrieval, and distribution of documents, and is particularly directed to methods and apparatus for electronically handling revisions or other modifications to documents.
2. Background of the Invention
Document storage, retrieval and distribution systems which store documentation in electronic format have been known for some time. Known systems may include document scanners which capture and binarize images of the documents, data compressors for storing the images in compressed format to reduce the amount of storage needed various types of memory for storing the images, and networks to permit remote access to the stored documents for viewing and hardcopy printing. Typically, magnetic memory is used for short-term storage and optical disks are used for long-term archival storage.
The type of documents with which these systems are used may encompass any type of graphics or writing on paper. The documents typically range from 81/2".times.11" office type documents with text and/or graphics, to large E sized (34".times.44") engineering or architectural drawings.
There is a trade-off in the scanning-binarization process: capture of fine detail in a document requires high resolution scanning and is relatively expensive to produce because a larger number of data bits are generated and stored. As an example, an E sized document is approximately 1500 square inches. Scanning one E sized document with 200 bit/inch scan resolution requires 1500.times.200.times.200=60 million bits.
In one document retrieval application, such a system was used to capture and store the images of several hundred thousand engineering drawings and blueprints ranging from A size (81/2".times.11") to E size (34".times.44"). The images of individual drawings could be remotely accessed by engineers as needed, In the application, the goal was to allow the option of using a means for modifying documents, both at the central system site and at remote sites. Although documents could be electronically modified at the central site, document modification made at remote sites or by third parties off site had to be performed in the conventional, manual manner: erasing and redrawing.
In the past, document storage, modification and retrieval of modified documents has been done in several ways.
Traditionally, modifications have been made by erasure and addition to a paper original document. This technique is not labor or capital intensive but does not lend itself to document modification at remote sites (since an original document would be required at each site) or to electronic retrieval. A significant problem with modifications to the master original document is that the original often becomes soiled or smudged or folded and information can be buried in the dirt or crease.
Electronic modification and storage of documents could be done on a remotely located raster editing terminal. However, it would be necessary to have a raster editing terminal wherever the modifications might be made. In the situation where modifications are made by third parties it often is not feasible to compel the third party to purchase and install a raster editing terminal. Moreover, raster editing terminals can be expensive.
A third method of modifying documents is to use a computer-aided design (CAD) approach. With a CAD system, once a CAD document model has been created and stored, modifications can be made remotely without the expense of a raster editing terminal. The problem is that creating the CAD model from an existing document is extremely labor intensive. Where several hundred thousand documents are involved, the time and labor cost of creating CAD models for each document can render CAD unfeasible.
A fourth method of modifying documents and storing the modifications is to produce a hardcopy print of the original drawing, manually performed the modifications in the conventional manner by erasure and pencil additions, and then re-scan the modified document. The problem with this method is that with each print-modify-rescan cycle the scanned image experiences a further degradation, limiting the number of times this cycle can be performed, as higher generation scans quickly become unreadable.